This invention relates to a device for the separation of solid objects from a fluid flowing in a conduit tube, comprising a housing mounted between separate parts of the tube, which housing comprises a tubular outer wall and a tubular inner wall of a rotation-symmetrical basic shape, a ring-shaped collecting space being delimited between said walls, and a central body of a rotation-symmetrical basic shape placed concentrically relative to the inner wall, which central body at an inlet end cooperates with a first fluid converting device having the purpose of transforming an arriving axial fluid flow into a substantially rotating flow in a ring-shaped space between the central body and the inner wall, and at an outlet end cooperates with a second flow converting device with the purpose of transforming the rotating fluid flow in the latter ring space into an outgoing axial flow in the tube part that is located downstream of the housing, the inner wall having passages through which objects of a larger density than the fluid and carried by the fluid may pass radially outwards to be collected in a bottom of the collecting space.
A separator device of the type given above has been previously tested for use in nuclear power plants, more precisely in the feed water circuit to nuclear reactors of the boiler type. This arrangement is denominated particle or scrap trap by the men skilled in art. A primary object of the arrangement is to separate solid objects which accidentally have come into the feed water circuit and which may lead to problems in the plant, e.g., clogging of gaps at the control rods of the reactor or in fuel assemblies. The objects in question may be, e.g., screws, nuts, springs or similar, which are of a solid nature and have a larger density than the water. The previously tested separator arrangement is based on the use of a separator housing whose inner wall is formed with a passage with the form of a ring-shaped, circumferential gap. However, a considerable disadvantage of this construction is that the ring gap forms a circumferential interruption in the inner wall, whereby the downstream edge of the gap causes disturbances, such as turbulence and the creation of vortices in the main water flow that passes through the separator arrangement. Also the secondary flow that is taken out via the ring gap is disturbed to a high degree. Thus, rather intense vortex formations and turbulence arise in the collecting space outside the inner wall, which in practice results in that the objects that have been led out into the collecting space, after a shorter or longer period of time are carried away by the water and returned to the main flow. In other words, the capability of the arrangement to separate and keep objects becomes mediocre and occasionally non-existent, primarily with regard to lighter objects.
Further, in EP 0 162 441 a separator device is disclosed which in first hand may be used for the separation of steam from water. Also in this case, the separation takes place via a ring-shaped gap, to which must be added that the device does not comprise any collecting space in which solid objects would be trapped and accumulated.
The present invention aims at removing the above-mentioned inconveniences of the previously known separator device and creating an improved separator device. A primary object of the invention is to create a separator device that may not only trap the solid objects that are brought by the main flow in an effective way, but also to guarantee that the trapped objects reliably remain in the collecting space during a long time, preferably during the time that goes by between two consecutive reactor revisions. Another object is to create a separator device which, when it is passed by the main fluid flow, does not give rise to flow disturbances, such as vortex formations, turbulence and similar, which in turn may cause detrimental vibrations in the conduit system downstream of the device. A further object of the invention is to create a separator device of a mechanical construction that is as simple as possible, it being possible to mount the device into existing conduit tubes. Yet another object is to create a separator device that does not cause a considerable pressure drop in the main fluid flow when it passes through the device.
According to the invention, at least the primary object is achieved by means of the features that are defined in the characterizing clause of claim 1. Advantageous embodiments of the device according to the invention are further defined in the dependent claims.
Centrifugal separation devices for general industrial purposes have been previously disclosed in, e.g., U.S. Pat. Nos. 1,931,193, 193, 2,425,110, 2,512,253, 2,616,563, 2,986,278, 4,834,887, EP 0 005 494, EP 0 162 441 and EP 0 267 285. However, none of these devices are based on the use of tangentially separated, elongated holes of the type that characterizes the present invention. For this reason, the previously known devices are not suited for the separation of scrap from the feed water to nuclear reactors.